Electroluminescent techniques and devices

ABSTRACT

New electroluminescent techniques and devices are disclosed which render a product that is more commercially saleable, reliable, and economically feasible than heretofore was the case in the art. A stacked, multi-layered electroluminescent device is generally provided, comprising a first supporting layer or sheet of Mylar, for example, a front electrode that is transparent or at least translucent to visible light, a phosphor-filled layer of dielectric material, an additional dielectric layer if desired, and a rear electrode plate. Disposed in intimate contact with the front electrode and preferably between the electrode and the phosphor-filled layer is a web of electrically conductive filaments to obviate deleterious effects of electrode separations. The provision of a photo-sensitive electrically conductive material as the rear electrode is contemplated, which material can be photographically exposed and then developed so as to produce any desired pattern or configuration of electroluminescence. The phosphor-filled layer itself is contemplated to comprise a chemically inert layer of polypropolyene, for example, this layer being made electrically conductive by the insertion of a plurality of electrically conductive particulates dispersed throughout so as to thereby effectively control the dielectric constant thereof. Desirably, the electrically conductive particulates comprise phosphor particles novelly processed to include an adsorbed layer in the form of a glass coating thereon, the glass coating itself being provided with a discontinuous layer of stannous oxide.

United States Patent Leach [451 June 27, 1972 [54] ELECTROLUMINESCENT 21Appl. No.: 7,157

Primary Examiner-Herman Karl Saalbach Assistant Examiner-Wm. H. PunterAttorney-Jacobi, Lilling & Siegel [57] ABSTRACT New electroluminescenttechniques and devices are disclosed which render a product that is morecommercially saleable, reliable, and economically feasible thanheretofore was the case in the art. A stacked, multi-layeredelectroluminescent device is generally provided, comprising a firstsupporting layer or sheet of Mylar, for example, a front electrodethatis [5 2] [1.5. CI. ..3l3/108 A, 96/36.1, 117/215 transparent or at leasttranslucent to visible light, a phosphor- [51] Int. Cl. ..H0l j 1/62filled layer of dielectric material, an additional dielectric layer [58]Field of Search ..3l3/108, 108 R, 108 A; 96/49, if desired, and a rearelectrode plate. Disposed in intimate 96/36.1; 29/572; 117/21 1, 215contact with the front electrode and preferably between the electrodeand the phosphorfilled layer is a web of electrically References Citedconductive filaments to obviate deleterious effects of electrodeseparations. The provision of a photo-sensitive electri- UNITED STATESPATENTS cally conductive material as the rear electrode is contem-3,475,640 lO/1969 Litank ..313/108 p which material can bePhotographically exposed and 3,368,099 2/1968 Arnold... ...313/108 thendeveloped so as to produce any desired pattern or con- 3,310,703 3/1967Brooks 313/108 figuration of electroluminescence. The phosphor-filledlayer 2,885,560 5/1959 Destriau 313/108 itself is contemplated tocomprise a chemically inert layer of 3,376,453 4/1968 Leach 313/108polypropolyene, for example, this layer being made electri- 3,371,243 2/1968 Braml'ey. 315/169 cally conductive by the insertion of a pluralityof electrically 3,379,927 4/1968 Yando ..315/55 conductive particulatesdispersed throughout so as to thereby 3, 9 7/ R mm 117/215 effectivelycontrol the dielectric constant thereof. Desirably, 2,972,303 1961 Koy..-- the electrically conductive particulates comprise phosphor2,772,160 1 1/1956 p 49 particles novelly processed to include anadsorbed layer in the 3,005,708 10/1961 l-lesse ..96/36.l f f a glasscoating thereon, the glass coating it lf being 2,873,189 2/1959 Evans..96/36.1 provided with a discontinuous layer f Stannous i 2,756,1677/1956 Barnett ..96/36.l

11 Claims, 4 Drawing Figures f IO vise l [2 q k 7 22 1ELECTROLUMINESCENT TECHNIQUES AND DEVICES BACKGROUND OF THE-INVENTIONThis invention generally relates to electrolurninescence andparticularly concerns novel electroluminescent techniques and structurecontemplated to provide a more commercially saleable, reliable, andeconomically feasible electroluminescent device than heretofore waspossible in the art.

A particularly promising area of environmental utilization forelectroluminescent devices is to be found in the advertising industryspecifically as concerns the employment of electroluminescent devices inadvertising displays, signs and the like, and as further concerns thereplacement of commonly utilized neon-tube illuminating devices withelectroluminescent apparatus. To date, however, the state of the art,particularly when viewed from a commercial standpoint, has not been ableto provide the technology by which the use of electroluminescent devicesin such environments would be feasible.

This failure is not at all surprising when one considers the peculiarrequirements in this contemplated environment. For example, anelectroluminescent device that is desired to be utilized in anout-of-doors display would be subjected to thermal shocks," and bendingor ilexure stresses as well as to excessive amounts of moisture andother efficiency degrading substances. Specifically, theelectroluminescent devices now generally available typically comprise aplurality of stacked adjacent layers formed of difierent materialshaving different coefficients of expansion, and when a device of thistype is subjected to thermal shock, the various layers expand orcontract in differing amounts and tend to pull apart. More im portantly,the different degrees of expansion oftentimes creates cracks or areaseparations of the very thin transparent front electrode which isemployed in these devices, thus rendering the devices inoperative.

Further, the typical layered-type of electroluminescent device is highlysucceptable to moisture and vapor degradations and, as such, suchdevices cannot feasibly be utilized in high moisture environments suchas the out-of-doors. As is known, in devices of this type, free zinctends to be liberated from phosphor particles and/or the phosphor, andthis zinc is available for organic reaction with the dielectric layer.This reaction results in a darkening of the dielectric in the area ofthe reaction thereby decreasing the effective light output of the unit.Additional problems concerning the light output arises in connectionwith the destructive effect of reactable oxygen with the phosphorparticles themselves. If moisture is permitted within the area of thephosphor particles, then, due to the ionization which takes place withinthe device during normal operation thereof, oxygen from the moisture orwater particles tends to become free for reaction with the phosphor. Theoxygen reacts photochemically with the phosphor grain, thereby darkeningthe same.

Electroluminescent devices desired to be utilized in advertisingdisplays, for example, generally would have to generate somepredetermined pattern or display configuration to meet the requirementsof the user. For example, if electroluminescent devices were desired tobe utilized as replacements for neon lettering, the electroluminescentdevice in and of it self must serve to generate the required letter orletters. Furthermore, esoteric advertising effects which can presentlybe effected with neon tube techniques must also be reproducable by theelectroluminescent replacement, yet, the current state of the art hasnot produced any such electroluminescent device.

SUMMARY OF THE INVENTION Thus, as should be apparent, a need exists forelectroluminescent technology which will obviate the aforementioneddisadvantages of the currently available electroluminescent devices andspecifically which will enable the utilization of electroluminescentdevices as advertising displays and the like. It is the primary objectof the instant invention to provide the technology to satisfy this need.However, it should be understood at the outset that, while thisinvention is primarily directed to the adverfising industry, each of thetechniques disclosed herein have general widespread applicability.

It is an additional, though more specific, object of the instantinvention to provide an electroluminescent device which is substantiallyfree from the degrading efiects of moisture and the like.

It is a further object of the instant invention to provide anelectroluminescent device which can be readily constructed in aneconomical manner and which will generate predetermined patterns anddisplays of illumination.

It is another object of the instant invention to provide a newmanufacturing technique as well as materials for the phosphor-filledlayer of the stacked, multi-layer electroluminescent device, whichmaterials serve to increase the light output of the device, increase thelifetime of the device, and render the device suitable for constructionby mass-production techniques.

A further advantageous object of the instant invention concerns theprovision of an electroluminescent device of the type described which iscapable of withstanding thermal stresses and shocks as well as bendingand flexure stresses that normally would tend to render a deviceinoperative by creating cracks or area separations of the thinlight-transmitting front electrode provided.

Now, these objects as well as other objects which will become apparentas the description proceeds are implemented by the instant inventionwhich, from a general configurational format, will be seen to comprise amulti-layer unit including a first supporting layer or sheet of Mylar,for example, upon which the remaining layers of the stacked, multilayerdevice is constructed. A light-transmitting, such as at least atranslucent though preferably transparent, front electrode is thenprovided, this electrode being constructed of materials such asvaporized gold, silver or aluminum having typical thicknesses of 300 400angstroms. Of course, other electrode materials could be utilized ifdesired, one such material being micronsized glass spheres, the glassspheres being rendered electrically conductive by the provision of ametalized coating thereon.

Beneath the light-transmitting front electrode, a phosphorfilleddielectric layer is provided, the dielectric layer being formed of atranslucent dielectric material which, in the prefered inventiveembodiment, will be seen to comprise a chemically inert material such aspolypropolyene, for example, this layer being electrically conductive bymeans of the random dispersion therein of micron-size conductiveparticulates such as copper, silver, aluminum and the like. Underneaththe phosphor-filled layer, as additional dielectric layer may beprovided, if desired, and, subsequently, a rear electrode completes thestacked package.

As briefly alluded to above, one important feature of the instantinvention concerns the particular materials utilized in thephosphor-filled dielectric layer and specifically, the construction ofthis layer in and of itself. As mentioned above, a specific deficiencyof prior art devices concern their suseptability to the degradingetfects of moisture and particularly the resultant chemical reactionwhich takes place between the free zinc liberated from the phosphorparticles and the surrounding dielectric layer. The instant inventionproposes to utilize a chemically inert material as the dielectric layer,this chemically inert material preferably comprising polypropolyenealthough Teflon and polyethylene have also been found to be suitable.

Yet, a chemically inert dielectric material such as the materials underconsideration, although eliminating the deleterious chemical reactions,is not adequately electrically conductive material, and, accordingly,does not inherently serve to distribute the ionic current throughout thephosphor dispersed therein. The instant invention, however, contemplatesthe elimination of this disadvantagous feature while still retaining theadvanatages associated with chemical inertness by providing a randomdispersion of micron-size conductive particulates of such material ascopper, silver, or aluminum, for example, throughout the chemicallyinert dielectric. Accordingly, a psuedo dielectric is formed in whichthe phosphor particulates are dispersed, this psuedo dielectric havingoutstanding capabilities and physical characteristics and having acontrollable dielectric constant.

In an alternative form of the dielectric layer; the need for separateelectrically conductive particulates randomly dispersed throughout isobviated, as the phosphor particles themselves are contemplated toprovide the necessary electrical conductivity for properelectroluminescent operation. With this aspect or form of the instantinvention, the phosphor particles are contemplated to be treated in aparticular manner such that they can be coated with a glass layerresulting in phosphor particles having a substantially monomolecularglass coating rendering the particles insensitive to the effect ofenvironmental moisture or vapor. In this respect, the instant inventioncontemplates an improved processing treatment for the phosphor particleswhich comprises extruding a blend of the same with a particular glassfrit which melts at a temperature of between 800 900 F. and is free oflead or cadmium which would react with the sulfide in the phosphorgrains to form an undesirable chemical reaction, a polyethelene resin ora like being utilized as a binder during the extrusion procedure. Therod or wire thus produced is fed through a plasma or flame gun to spraythe same into a collector thereby melting the glass and coating thephosphor particles with the desired substantially monomolecular layer.

The glass covered phosphor particles are further contemplated to besprayed with a stannous chloride material which converts to form apartially conductive coating of stannous oxide. Alternatively, since theparticles eminating from the flame or plasma gun are at the desiredtemperature, they may be sprayed directly into an atmosphere of stannouschloride whereby the partial coating of conductive stannous oxide willbe simultaneously effected.

The glass coated, partially conductive, stannous oxide coated phosphorparticles so formed in this manner may then be mixed with a suitabledielectric material, such as the chemically inert polypropolyenediscussed above, to form the phosphor-filled dielectric, the conductivecoating on the glass particles accordingly eliminating the need for-theinsertion of additional conductive particulates into the chemicallyinert dielectric material. As should be apparent, the dielectricconstant of the material utilized can be varied as necessary either bythe insertion of the additional conductive particulates or by theutilization of coated phosphor particulates as above described.

In accordance with yet another important aspect or embodiment of theinstant invention, a web or mat of conductive filaments is contemplatedto be placed in intimate contact with the light-transmitting frontelectrode. The web or mat, in the preferred inventive embodiment,comprises minute micronsize filaments constructed of conductive materialsuch as copper, aluminum, silver, stainless steel, or glass or quartzhaving a coating of stannous oxide, these filaments being randomlydispersed preferably between the front electrode and the underlyingphosphorfilled dielectric layer. As discussed above, thermal shocks andbending stresses oftentimes create cracks or area separations within thethin transparent front electrode, these cracks or separations renderingthe device unusable. However, the random dispersion of conductivefilaments contemplated herein eliminates this problem for, if a crack orarea separation in the thin front electrode should occur, the conductivefilaments themselves will bridge the gap and insure the continueddistribution of elec trical voltage potential throughout the desiredlighting area. This aspect of the invention in and of itself representsa significant advance in the art and can provide an electroluminescentdevice suitable for use in aggravated environments.

7 In accordance ,with yet another particularly advantageous aspect ofthe instant invention, the rear or back electrode of the device iscontemplated to be constructed of a photo-sensitive yet electricallyconductive coating. This coating is contemplated to be exposed toelectromagnetic energy such as light, for example, which may betransmitted through a screen or a negative so as to impinge upon thephoto-sensitive coating in any desired pattern or configuration. Thephoto-sensitive coating is then developed by the application of suitabledeveloping chemicals which results in the removal of all except thedesired portions of the rear electrode. Accordingly, complex areadesigns can readily be created on the rear electrode of theelectroluminescent device causing the device to generate light only indesired areas and in any configuration or pattern. This feature of theinstant invention widely expands the field of use of electroluminescentdevices perse as, for the first time, any pattern or light generatingconfiguration canbe created at will, economically, and without requiringprefabrication or physical cutting of rear electrode patterns.

BRIEF DESCRIPTION OF THE DRAWINGS The invention itself will be betterunderstood and further advantageous features thereof will becomeapparent from the following detailed description of a preferredinventive embodiment, such description making reference to the appendedsheets of drawings, wherein:

FIG. 1 is a perspective view, partially in section and partially brokenaway for a illustrative clarity, depicting the overall constructionalfeatures of the instant invention;

FIG. 2 is a perspective illustration, also partially in section,depicting the novel process disclosed herein whereby, throughphotographic techniques, the rear electrode of the device can be etchedsuch that the electroluminescent device will radiate or generate lightin any desired display, configuration or pattern;

FIG. 3 is a schematic, block diagram illustration of a novel processdisclosed herein whereby the phosphor particles utilized in thephosphor-filled dielectric layer are coated with glass and aresubsequently made conductive by means of a coating of stannous chloride,these particles being contemplated for utilization in the preferredinventive embodiment in a dielectric layer such as polypropolyene whichis chemically inert and which normally is electrically non-conducting;and

FIG. 4 is a sectional view of a phosphor particle with various coatingsthereon such as produced by the process of FIG. 3.

DETAILED DESCRIPTION OF PREFERRED INVENTIVE EMBODIMENTS Referring now tothe drawing, and particularly to FIG. 1 thereof, a preferredconstruction of the novel electroluminescent device is illustrated, thisdevice being of the stacked, multi-layer variety. Specifically, thenovel electroluminescent device will be seen to comprise a firstsupporting layer or sheet 10 formed of a substantially moisture-proof,at least translucent or transparent insulating material such as Mylar(polyethylene terephthalate) or Saran (vinylidene chloride), althoughother obvious insulating layers can be readily substituted therefore.The supporting layer or sheet comprises a major portion of the thicknessof the overall device and, in accordance with the preferredconstructional technique, is utilized as the starting material in thefabrication of the device.

A front electrode 12 is then provided and can either be sprayed orroller-coated to the supporting sheet 10. The front electrode must belight-transmitting, i.e. at least translucent, though preferablytransparent, such that radiant energy generated in the layersimmediately below can be transmitted there through. The front electrode12 is therefore constructed of materials such as vaporized gold, silver,or aluminum, having thicknesses in the range of 300 400 angstroms as istypical in the art. Other electrode materials could also be utilized, ifso desired, in accordance with the inventive concepts herein and, inthis respect, one such substitutional material could comprisemicron-size glass sphere which are rendered electrically conductive bythe provision of a metalized coating thereon.

Disposed generally below the front electrode 12 is a phosphor-filleddielectric layer 14 formed as a continuous layer containing theelectroluminescent phosphor particles 16. Immediately below thephosphor-filled dielectric layer 14, an additional dielectric layer 18is provided, the dielectric layer 18 preferably being reflective tolight. Finally, a rear electrode structure 20 is provided, formed of anelectrically conductive material and, if desired, although notillustrated, an electrically insulating, moisture-proof material orlacquer can be subsequently disposed beneath, and in intimate contactwith the rear electrode 20.

With the arrangement described immediately above, when an alternatingelectrical field (AC) is applied across leads 22 and 24 respectivelyconnected to the transparent front electrode l2 and to the rearelectrode 20, a light output is produced through the supporting sheet orlayer 10. The electrical field is established between theelectrically-conducting layers 12 and 20, and such field serves toexcite the electroluminescent phosphor particles 16 in thephosphor-filled dielectric layer 14. Accordingly, these particles emitlight and the light either passes directly outwardly through the layers14, 12 and 10, or first rearwardly to the reflective layer 18, and thenoutwardly through the layers 14, 12 and 10.

As briefly discussed above, certain aspects of the novel invention areconcerned with the particular materials and the construction utilized inand about the various layers of the multi-layered device of FIG. 1. Onesuch inventive aspect contemplates the provision of a web or mat ofconductive filaments 26 disposed in intimate contact with the thin,trans parent front electrode 12 and, preferably, between the frontelectrode 12 and the phosphor-filled dielectric layer 14. With thepreferred inventive construction, the web or mat of conductive filamentscomprises minute, micron-size filaments constructed of a conductivematerial such as copper, aluminum, silver, stainless steel, or glass orquartz with a coating such as stannous oxide. These filaments 26 arepreferably randomly dispersed throughout the expanse of theelectroluminescent device beneath the front, transparent electrode 12.

As discussed above, thermal stresses as well as bending or flexurestresses to which the electroluminescent device is subjected oftentimeswill create cracks or area separations in the thin, transparentelectrode 12, which cracks or area separations can render theelectroluminescent device inoperative or, at the very least,substantially reduce the light generating areas thereof. The conductivefilaments 26, however, effectively serves to bridge the gap" between anycrack or electrode area separation and thus renders the device capableof withstanding such abusive stresses. The light output from the deviceis not at all reduced by the provision of the random dispersion ofconductive filaments 26 due to the minute size of such filaments and, inthe fabrication of the device, these filaments can literally besprinkled" over the conducting electrode 12 prior to the application ofthe phosphor-filled dielectric layer 14. While the disposition of themat or web of conductive filaments 26 has been indicated to preferablylie between the front transparent electrode 12 and the phosphorfilleddielectric layer 14, it should be understood that, from a conceptualstandpoint, the prime requirement as to disposition of the conductivefilaments is that the conductive filaments be in intimate contact withsuch front electrodes so as to insure the even disposition of electricalpotential throughout the electrode area. The provision of the conductiveweb or mat 26 in and of itself constitutes a major advance in the art,widely expanding the possible environments of utility of anelectroluminescent device.

Consistent with the prime objectives of the instant invention to providea device suitable for utilization in the advertising industry, the novelinventive device incorporates constructional features by which thedevice can generate radiant energy in any desired display, configurationor pattern. For example, and again referring to FIG. 1, let it beassumed that one would desire the electroluminescent devices depictedtherein to radiate light only the pattern of a letter such as the letterA, for example, as shown in dotted lines, through the supporting sheetor layer 10. To achieve this effect, the instant invention contemplatesthe provision of a rear electrode 20 constructed not only to beelectrically conductive, but to also be photosensitive. In this respect,the rear electrode 20 comprises a photosensitive coating which containsa mixture of electrically-conductive particulates which, in thepreferred inventive embodiment, comprise approximately 20 percent byweight of the coating and has a grain size of approximately 3 to 20microns. The photo-sensitive coating itself is contemplated in thepreferred inventive embodiment to comprise cellulose acetate or vinylmethyl-ether/maleic-anhydride copolymer sensitized with a diazo whichitself may comprise and ester-amide of 2- diazol-naphthol-S-sulfonicacid.

The manner or technique by which the electroluminescent device of FIG. 1is caused to generate only selective patterns of light can best be seenby reference to FIG. 2 wherein the multi-layered device is againillustrated in perspective view and wherein like layers and componentshave identical reference numerals as those utilized with respect to thedescription of the device in FIG. 1.

Initially, a pattern or negative such as a mask 28 having a cutoutportion 30 in the shape of the desired letter A, for example, isdisposed between an optical system comprising a source of light 32 andan associated lens 34, and the rear electrode 20 of theelectroluminescent device itself. Radiant energy as schematicallyillustrated by lines 36 impinge from the light source 22 onto the rearelectrode 20 in the pattern or configuration defined by negative orcut-out portion 30 of the mask 28. In this manner, the photo-sensitiverear electrode 20 is exposed in the desired pattern or configuration ofsubsequent light generation. The non-exposed portions of the rearelectrode 20 are then chemically-developed and removed so as to actuallyform the depicted pattern of the letter A. In accordance with thepreferred inventive techniques, the chemical developer utilized iscontemplated to comprise, by volume, approximately 50 ozs. of gumarabic, 30 ozs. distilled water, and 20 ozs. of methanol. During thedeveloping procedure, the undesired electrode area is removed and theremaining portions of the electrode covered with a lacquer, which isfilled with conductive particulates. Alternatively, the chemicaldeveloper could itself incorporate the lacquer and, in the instance, thechemical developer is contemplated to comprise by volume, approximately60 ozs. of ethylene dichloride, 20 ozs. of epoxy resin, and 20 ozs. ofelectrically-conductive particulates, which particulates assist in thedistribution of current and potential throughout the remaining portionof the rear electrode 20. The epoxy resin of the developer itself couldcomprise an unmodified hydroxl containing resinous glycidyl polyether ofa dihydric phenol. As a further alterna tive, and from a more generalstandpoint, the chemical developer incorporating the lacquer couldcomprise, by volume, 60 ozs. of ethylene dichloride, 20 ozs. ofelectricallyconductive particulates, as well as 20 05. of polyvinylalcohol, vinyl acetate or emulsions of both vinyl and acrylic. Ofcourse, other suitable chemical developers and the like will be apparentto those of ordinary skill in the art.

The phosphor-filled dielectric layer 14 itself constitutes an importantaspect of the instant invention significantly contributing to theoverall efi'rciency and reliability of the novel device in its field ofintended use. The phosphor-filled dielectric layer, as mentioned above,includes the phosphor particles 16 carried within and randomly dispersedthroughout a dielectric matrix 38 such as is shown in FIG. 1. Thedielectric material 38 must be translucent, or transparent for optimumefficiency and, this layer should preferably be chemically inert so asto make the overall device less susceptible to the degrading effects ofmoisture, and particularly to eliminate the possibilities of chemicalreactions which take place in ordinary devices between free zincliberated from the phosphor articles and the surrounding dielectriclayer. In this respect, the instant invention contemplates to utilize asthe dielectric layer a chemically inert material preferably comprisingpolypropylene although Teflon and polyethylene have also been found tobe suitable.

Yet, a chemically inert dielectric such as the polypropylenecontemplated for use is not a good enough conductor of electricity toinsure the proper ionic current flow throughout the layer enablingoperation of the device. Accordingly, the instant invention contemplatesthe provision of a random dispersion of micron-size conductiveparticulates 40 throughout the dielectric layer, these conductiveparticulates rendering the chemically inert dielectric materialsufficiently electrically-conductive. Suitable materials for utilizationas the conductive particulates have been found to comprise copper,silver, aluminum and the like although other metallic ingredients couldbe substituted therefore.

As an alternative to the utilization of separate electricallyconductiveparticulates 40 throughout the chemically inert dielectric layer 14, thephosphor particles 16 can themselves be provided with apartially-conductive discontinuous coating of metallic material.However, before an explanation is set forth as to the manner ofproducing such an electrically conductive discontinuous coating 42 onthe phosphor particles 16 as shown in FIG. 4, a further feature oftheinvention will be discussed, this feature being concerned with theprovision of a coating on the phosphor particles intermediate thephosphor particles and the electrically-conductive material, whichcoating is moisture-proof and vapor-proof thereby rendering theparticles insensitive to deterioration in this respect and acting incooperation with the chemically inert dielectric material 38 to reducethe overall degrading effects of moisture.

To this end, the phosphor particles 16 may be provided with a coating ofmethylchlorosilanes or colloidal silicate, but according to a preferredembodiment of this invention, the phosphor grains are encapsulated in asubstantially monomolecular glass coating. To provide themethyclorosilane coating, the phosphor particles are bathed in amethylchlorosilane solution and then separated and dried, the coating,when adsorbed by the phosphor particles, assumes a polycarbon nature soas to effectively seal any moisture out of the phosphor particles.Moreover, the coating material itself replaces any moisture content inthephosphor particles initially since the phosphor particles have 'agreater affinity for methylchlorosilane than for water, i.e. there is abi-functional condensation. Additionally, the adsorbedmethylchlorosilane coating traps any free zinc within the peripherallimits of the particle so as to again act in conjunction with thechemically inert dielectric to prevent any adverse che micalreaction.The thickness of the coating rovided over the phosphor particles iscontemplated to be a minor fractional part of the mean max-- imumdimension of the phosphor particles and, in fact, tends to be of theorder of one molecule. I 1

As mentioned above, however, the. preferred intermediate coating betweenthe phosphor particles and discontinuous electrically conductive coatingcomprises glass as indicated by reference numberal 44 in FIG. 4. Thepreferred and novel technique for forming such glass-coated phosphorparticles is illustrated in FIG. 3 and attention is therein directed.The phosphor particles are initially intimately intermixed in anyconventional manner with a frit which must have a melting point ofbetween 800 and 900 F. and be free of lead and cadmium toavoid any colorreaction, and a binder which may be in the form of polyethylene or thelike, at the station in the block diagram of FIG. 3 indicated byreference 46. This mixtional extruding mechanism as schematically shownat 48 to form an elongated filament or rod which may be stored on reelsat station 50 or otherwise prepared in any desired manner for feeding toa conventional flame'or plasma gun designated generally by reference No.52. A detailed explanation of this apparatus is not necessary since thesignificant factors to be considered comprise merely the subjection ofthe elongated rod of phosphor particles, frit and binder to an elevatedtemperature within the plasma or flame gun'52 prior to the expulsion ofthe heated mixture from the flame gun in the form of a spray indicatedschematically by line 54 which is ing from the plasma or flame gun 52 isapproximately in the range of about 900 to l,000 F.

Now, the glass-coated phosphor grains are contemplated to be furtherprocessed so as to provide the partial or discontinuous electricallyconductive layer 42 referred to hereinabove with reference to FIG. 4.This may be achieved in accordance with a variety of novel techniques asillustrated in FIG. 3. For example, the individually glass-coatedphosphor particles may be separately subjected to a stannous chlorideatmosphere in a further processing station 58 by passing the samethrough a spray of stannous chloride, which stannous chloride sprayimpacts on the glass-coated phosphor at a point in time when the glasscoating is still heated in the range of 900 to 1,000 F. Accordingly, thecarefully selected glass formulation would react with the stannouschloride to form stannous oxide which is partially conductive as isrequired to insure electrical conductivity of the chemicall inertdielectric material 38 in which the phosphor particulates are dispersed.The amount of conductivity imparted to the conductive coating 42 on thephosphor particle 16 can be controlled by manipulation of thetemperature of the spray, solutionstrength, formulation of the glass,and actual point of impact of the two spray patterns. As

a result, the partial or discontinuous layer 42 can be formed such thatits conductivity is sufficient to insure that only an ionic current flowcan exist and that a continuous conductive path is not present.

Alternatively, since the spray 54 eminating from the gun is at a desiredtemperature, the stannous chloride atmosphere may be provided in thecollector 56 from a source 60 whereby the discontinuous stannous oxidecoating will be concomittantly provided in addition to the glass coatingon the phosphor particles.

In any event, the insertion of additional conductive particulates intothe chemically inert dielectric layer or the alternative provision of adiscontinuous conductive coating on the phosphor'particulates themselvesprovides the possibility of controlling the dielectric constant of thechemically inert material '38 in any desired fashion to insure thedesired amount of ionic current flow and distribution. Thus, theadvantages of a chemically inert material with respect to eliminatingboth the degrading effects of moisture and vapor as well as thedarkening effects of undesired zinc reactions can be retained while thenormally poor electrical conductivity of chemically inert materials isobviated.

As should now be apparent, the objects initially set forth at the outsetto the specification have been successfully achieved. Accordingly,

What is claimed is:

1. In an electroluminescent device of the type including a plurality ofstacked layers defining at least a light-transmitting supporting sheet,a light-transmitting front electrode, a phosphor-filled layer, and arear electrode, the improvement comprising: a separate layer defining aweb of electrically conductive filaments dispersed in intimate contactwith said front I electrode.

'ture of phosphor, frit and binder is fed through any conven- It hasbeen found that the temperature of the spray 54 eminat- 2. Theimprovement defined in claim 1, wherein said electrically conductivefilaments are randomly dispersed.

3. The improvement defined in claim 1, wherein each filament has athickness of the order of one micron.

4. The improvement defined in claim 3, wherein said web is disposedbetween said front electrode and said phosphor-filled layer. I

5. The improvement defined in claim 4, wherein said filaments areconstructed of materials selected from the group consisting of copper,aluminum, silver, stainless steel, and glass or quartz with a coating ofstannous oxide.

6. In an electroluminescent device of the type including a plurality ofstacked layers defining at least a light-transmitting suppor'dng sheet,a light-transmitting front electrode, a phosphor-filled layer, and arear electrode, the improvement wherein said rear electrode isconstructed of a photo-sensitive, electrically conductive coating.

coating are chemically removed thus defining an electrode pattern, andwherein said conductive particulates comprise 20 percent by weight ofsaid photo-sensitive coating and have a grain size of approximately 3 to20 microns.

10. The improvement defined in claim 9, wherein said photo-sensitivecoating comprises materials selected from the group consisting ofcellulose acetate or vinyl methylether/maleic-anhydride copolymersensitized with a diazo.

11. The improvement defined in claim 10, wherein the diazo comprises anester amide of 2-diazo-l-naphthol-5-sulfonic acid.

1. In an electroluminescent device of the type including a plurality ofstacked layers defining at least a lighttransmitting supporting sheet, alight-transmitting front electrode, a phosphor-filled layer, and a rearelectrode, the improvement comprising: a separate layer defining a webof electrically conductive filaments dispersed in intimate contact withsaid front electrode.
 2. The improvement defined in claim 1, whereinsaid electrically conductive filaments are randomly dispersed.
 3. Theimprovement defined in claim 1, wherein each filament has a thickness ofthe order of one micron.
 4. The improvement defined in claim 3, whereinsaid web is disposed between said front electrode and saidphosphor-filled layer.
 5. The improvement defined in claim 4, whereinsaid filaments are constructed of materials selected from the groupconsisting of copper, aluminum, silver, stainless steel, and glass orquartz with a coating of stannous oxide.
 6. In an electroluminescentdevice of the type including a plurality of stacked layers defining atleast a light-transmitting supporting sheet, a light-transmitting frontelectrode, a phosphor-filled layer, and a rear electrode, theimprovement wherein said rear electrode is constructed of aphoto-sensitive, electrically conductive coating.
 7. The improvement inclaim 6, wherein selected portions of said photo-sensitive coating arechemically removed thus defining an electrode pattern.
 8. Theimprovement defined in claim 7, wherein said photo-senstiive coatingcontains a mixture of electrically conductive particulates.
 9. In anelectroluminescent device of the type including a plurality of stackedlayers defining at least a light-transmitting supporting sheet, alight-transmitting front electrode, a phosphor-filled layer, and a rearelectrode, the improvement wherein said rear electrode is constructed ofa photo-sensitive coating containing a mixture of electricallyconductive particulates, wherein selected portions of saidphoto-sensitive coating are chemically removed thus defining anelectrode pattern, and wherein said conductive particulates comprise 20percent by weight of said photo-sensitive coating and have a grain sizeof approximately 3 to 20 microns.
 10. The improvement defined in claim9, wherein said photo-sensitive coating comprises materials selectedfrom the group consisting of cellulose acetate or vinylmethyl-ether/maleic-anhydride copolymer sensitized with a diazo.
 11. Theimprovement defined in claim 10, wherein the diazo comprises an esteramide of 2-diazo-1-naphthol-5-sulfonic acid.